| 1. |
|
|
| 2. |
|
|
| 3. |
- Härdelin, Linda, 1977, et al.
(författare)
-
Electrospinning of cellulose nanofibers from ionic liquids: The effect of different cosolvents
- 2012
-
Ingår i: Journal of Applied Polymer Science. - : Wiley. - 1097-4628 .- 0021-8995. ; 125:3, s. 1901-1909
-
Tidskriftsartikel (refereegranskat)abstract
- Cellulose was electrospun with various concentrations of ionic liquid and cosolvent. Three different cosolvents were used in this study; dimethylacetamide (DMAc), dimethyl formamide (DMF), and dimethyl sulfoxide (DMSO). The cosolvents were added to modify the viscosity, electrical conductivity, and surface tension of the solutions. The solubility of cellulose in ionic liquids is highly affected by changes in solvent properties on the molecular level in the binary solvent systems. The difference in molecular structure of the cosolvents and the interactions between cosolvent and ionic liquid can explain the difference in dissolution power of the cosolvents. Scanning electron microscope (SEM) was used to characterize electrospun cellulose fibers. For the systems tested the importance of having a rather high viscosity and high surface tension, and some degree of shear thinning to produce fibers is shown.
|
|
| 4. |
|
|
| 5. |
|
|
| 6. |
|
|
| 7. |
|
|
| 8. |
- Härdelin, Linda, 1977, et al.
(författare)
-
Influence of molecular weight and rheological behavior on electrospinning cellulose nanofibers from ionic liquids
- 2013
-
Ingår i: Journal of Applied Polymer Science. - : Wiley. - 1097-4628 .- 0021-8995. ; 130:4, s. 2303-2310
-
Tidskriftsartikel (refereegranskat)abstract
- Dissolving pulp was depolymerized with 2.5M HCl into cellulose fractions with decreasing molecular weight relative to acid treatment time. The cellulose fractions were dissolved at various concentrations in the ionic liquid 1-ethyl-3-methylimidazolium acetate (EmimAc) with co-solvent DMSO at ratio 1 : 1 (w/w) and electrospun. Size exclusion chromatography was used to evaluate the molecular weight distributions and the rheological properties were characterized with a cone-and-plate rheometer. Scanning electron microscope was used to evaluate the fiber morphology, and thereby spinnability. Zero shear viscosity as a function of cellulose concentration show that all the solutions in this study are in the entangled semi-dilute regime; where the polymer concentration is large enough for significant overlap necessary for chain entanglement. However, within the intervals studied, neither cellulose concentration nor molecular weight seems to be decisive for if a solution can be electrospun into fibers or not. It is rather the viscosity of the solution that is decisive for electrospinnability, even though the solution is in the entangled semi-dilute regime.
|
|
| 9. |
- Stenhamre, Hanna, et al.
(författare)
-
Nanosized fibers' effect on adult human articular chondrocytes behavior.
- 2013
-
Ingår i: Materials science & engineering. C, Materials for biological applications. - : Elsevier BV. - 1873-0191 .- 0928-4931. ; 33:3, s. 1539-1545
-
Tidskriftsartikel (refereegranskat)abstract
- Tissue engineering with chondrogenic cell based therapies is an expanding field with the intention of treating cartilage defects. It has been suggested that scaffolds used in cartilage tissue engineering influence cellular behavior and thus the long-term clinical outcome. The objective of this study was to assess whether chondrocyte attachment, proliferation and post-expansion re-differentiation could be influenced by the size of the fibers presented to the cells in a scaffold. Polylactic acid (PLA) scaffolds with different fiber morphologies were produced, i.e. microfiber (MS) scaffolds as well as nanofiber-coated microfiber scaffold (NMS). Adult human articular chondrocytes were cultured in the scaffolds in vitro up to 28 days, and the resulting constructs were assessed histologically, immunohistochemically, and biochemically. Attachment of cells and serum proteins to the scaffolds was affected by the architecture. The results point toward nano-patterning onto the microfibers influencing proliferation of the chondrocytes, and the overall 3D environment having a greater influence on the re-differentiation. In the efforts of finding the optimal scaffold for cartilage tissue engineering, studies as the current contribute to the knowledge of how to affect and control chondrocytes behavior.
|
|
| 10. |
- Thorvaldsson, Anna, 1981, et al.
(författare)
-
Controlling the Architecture of Nanofiber-Coated Microfibers Using Electrospinning
- 2010
-
Ingår i: Journal of Applied Polymer Science. - : Wiley. - 1097-4628 .- 0021-8995. ; 118:1, s. 511-517
-
Tidskriftsartikel (refereegranskat)abstract
- This study shows that electrospinning nanofibers onto single microfibers allows for careful tailoring of material properties that may suit a wide variety of applications. The nanofiber-coated microfibers are created by electrospinning nanofibers alongside a microfiber toward a collector that rotates around the microfiber. This force the nanofibers to be collected around the microfiber, creating a hierarchical structure that can be modified at nano scale. In this study, control of nanofiber diameters, nanofiber alignment, and nanofiber loading was evaluated. It was seen that varying polymer concentration affected the nanofiber diameters, collecting the nanofiber-coated microfibers at different speeds changed the degree of alignment of the nanofibers and that changing the polymer feeding rate affected the loading density of the nanofibers collected. The carefully designed nanofiber-coated microfibers have great potential in creation of highly porous materials with tailored properties down to nano scale.
|
|
| 11. |
- Thorvaldsson, Anna, 1981, et al.
(författare)
-
Development of Nanofiber-Reinforced Hydrogel Scaffolds for Nucleus Pulposus Regeneration by a Combination of Electrospinning and Spraying Technique
- 2013
-
Ingår i: Journal of Applied Polymer Science. - : Wiley. - 1097-4628 .- 0021-8995. ; 128:2, s. 1158-1163
-
Tidskriftsartikel (refereegranskat)abstract
- In this work a new method is presented to efficiently produce hydrogel scaffolds reinforced with nanofibers to show enhanced mechanical properties and improved structural integrity. The method is based on a combination of air brush spraying of a hydrogel and electrospinning of nanofibers. With air brush spraying the controllability is enhanced and the potential for scale-up increased. The developed method was used to successfully reinforce gellan gum hydrogels with electrospun polycaprolactone nanofibers. Optical and rheological evaluations were performed and showed that parameters such as the amount of incorporated nanofibers, gellan gum concentration and calcium chloride (crosslinker) concentrations could be used to modulate material properties. Incorporation of a small amount of nanofibers had a reinforcing effect and resulted in a hydrogel with rheological properties similar to the human nucleus pulposus (NP). The method is flexible and carries potential for designing scaffolds for e. g. NP tissue regeneration. (
|
|
| 12. |
- Thorvaldsson, Anna, 1981, et al.
(författare)
-
Electrospinning of Highly Porous Scaffolds for Cartilage Regeneration
- 2008
-
Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 9:3, s. 1044-1049
-
Tidskriftsartikel (refereegranskat)abstract
- This study presents a new innovative method where electrospinning is used to coat single microfibers with nanofibers. The nanofiber-coated microfibers can be formed into scaffolds with the combined benefits of tailored porosity for cellular infiltration and nanostructured surface morphology for cell growth. The nanofiber coating is obtained by using a grounded collector rotating around the microfiber, to establish an electrical field yet allow collection of nanofibers on the microfiber. A Teflon tube surrounding the fibers and collector is used to force the nanofibers to the microfiber. Polycaprolactone nanofibers were electrospun onto polylactic acid microfibers and scaffolds of 95 and 97% porosities were made. Human chondrocytes were seeded on these scaffolds and on reference scaffolds of purely nanofibers and microfibers. Thereafter, cellular infiltration was investigated. The results indicated that scaffold porosity had great effects on cellular infiltration, with higher porosity resulting in increased infiltration, thereby confirming the advantage of the presented method. © 2008 American Chemical Society.
|
|
| 13. |
- Thorvaldsson, Anna, 1981, et al.
(författare)
-
Electrospinning of nanofibers for biomedical applications
- 2008
-
Ingår i: 8th World Biomaterials Congress 2008, WBC 2008; Amsterdam; Netherlands; 28 May 2008 through 1 June 2008. - 9781615670802 ; 3, s. 1197-
-
Konferensbidrag (refereegranskat)
|
|
| 14. |
- Thorvaldsson, Anna, 1981, et al.
(författare)
-
Superhydrophobic behaviour of plasma modified electrospun cellulose nanofiber-coated microfibers
- 2012
-
Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 19:5, s. 1743-1748
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, a method is presented for production of a textile cellulose fiber with non-wetting properties suitable for applications ranging from wound care and tissue engineering to clothing and other textile applications. Non-wettability is achieved by coating a textile cellulose microfiber with electrospun cellulose nanofibers, creating a large and rough surface area that is further plasma treated with fluorine plasma. High surface roughness and efficient deposition of covalently bound fluorine groups results in the fiber exhibiting non-wetting properties with contact angle measurements indicating superhydrophobicity (> 150A degrees water contact angle). It is an environmentally friendly method and the flexibility of the electrospinning process allows for careful design of material properties regarding everything from material choice and surface chemistry to fiber morphology and fiber assembly, pointing to the potential of the method and the developed fibers within a wide range of applications.
|
|
| 15. |
- Walkenström, Pernilla, 1969
(författare)
-
Phase Distribution of Mixed Biopolymer Gels in Relation to Process Conditions
- 1996
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The influence of various process parameters on the microstructure and rheological properties of pure and mixed gels of gelatin and whey proteins has been investigated. Gelatin is a cold-set protein and whey proteins are a group of thermo-set globular proteins. Depending on the charge present, whey proteins can form two types of gel structures. Particulate networks, with network strand dimensions in ~.my.m, are formed at pH-values within the isoelectric region (roughly between pH 4 and 6) and fine-stranded networks, with dimensions in nm, are formed above and below the isoelectric region. The microstructure has been characterised by light- and electron microscopy and further quantified by image analysis. The rheological properties have been characterised by viscoelastic measurements and tensile tests. Phase-separated, bicontinuous mixed gels are formed at pH-values within the isoelectric region of the whey proteins, when conventional heating and cooling are used as the gelling technique. The bicontinuous morphology is unaffected by changes in the polymer mixing ratio, while the rheological properties shift, i.e. at a low whey protein concentration, the mixed gels follow the properties of gelatin and vice versa. The bicontinuous morphology is also unaffected by shear in the initial stages of gel formation of the whey proteins, but the homogeneity is affected. A mixed gel with a broader pore size distribution in the whey protein network, and thereby larger domains of the gelatin phase, is created by the shear. When image analysis is used to quantify both pure and mixed networks, it is evident that the shear induces inhomogeneities. In relation to the rheological properties, suspensions sheared under controlled conditions form gels with storage moduli twice as high as those for unsheared gels. Using a combination of temperature and high-pressure processing as the gelling technique, the order of gel formation between the pure polymers is changed compared to that followed when using temperature only. In accordance with the changes in the order of gel formation, the bicontinuous morphology is shifted to a gelatin continuous morphology. Phase-separated bicontinuous mixed gels are formed at pH-values above the isoelectric region, when conventional heating and cooling are used as the gelling technique. As the mixing ratio is varied, a shift in rheological properties takes place, while no corresponding changes are found in the microstructure. When shear is used as a processing parameter for the mixed gels composed of fine-stranded whey proteins, no significant effects are found either in the microstructure or in the rheological properties. When the order of gel formation between the pure polymers is changed, using a combination of high-pressure processing and temperature for the gel formation, the bicontinuous morphology is shifted to a complex coacervate structure, composed of one single network structure. The complex coacervate shows a significantly higher storage modulus than the bicontinuous mixed network.
|
|
